Generally, you would disable an account to revoke sharing. Are you sharing these outside your domain? That could be part of the problem. I agree there should be an easier way to remove sharing for everything for a particular user (and there may be). Have you checked out GAM?
Yep, we're sharing outside your domain, but that's a feature that they advertise and recommend. I've started to check GAM, but what should have been a chore in our sprint has quickly turned into a fullblown story. I'll have to find some time to waste figuring out how to do this thing that I can't believe Google doesn't have built in.
When I search to:email@here.com it shows all the documents shared with that person, then I can Ctrl+a and click "share" and remove that person from all of them at once.
https://webapps.stackexchange.com/questions/52093/see-all-sh...
Generally, you would disable an account to revoke sharing. Are you sharing these outside your domain? That could be part of the problem. I agree there should be an easier way to remove sharing for everything for a particular user (and there may be). Have you checked out GAM?
https://github.com/jay0lee/GAM